Published: Sun, October 07, 2018
Sci-tech | By April Francis

Astronomers Discover Elemental Proof For A Moon Outside Our Solar System

Astronomers Discover Elemental Proof For A Moon Outside Our Solar System

They checked about 300 planets for any weirdness that might mean a moon.

Using the Hubble Space Telescope and the Kepler Space Telescope, astronomers have found the first compelling evidence for a Neptune-sized moon orbiting a giant gas planet 8,000 light-years away.

Kipping and Teachey combined the Kepler and Hubble data to build a model of the sun-planet-moon system.

"If confirmed by follow-up observations, the finding could provide vital clues about the development of planetary systems and may cause experts to revisit theories of how moons form around planets", he added.

Only two planets in our solar system - Mercury and Venus - don't have moons, Kipping said. "To be honest, we never really anxious too much about habitability, just because they're both gas giants".

"When we derived the mass ratio, that's really sort of what I would say, in court, defines the difference between a planet and a moon or a binary planet", he said.

"We saw little deviations and wobbles in the light curve that caught our attention", Kipping said.

[1] The moons of Jupiter and Saturn likely formed through the agglomeration into a disc of material orbiting the planets, so it is possible that this exomoon also formed in a circumplanetary disc.

In the meantime, a new release of Kepler data smoothed away many of those bumps, weakening the original case for a moon search. Kepler 1625b and its satellite, however, are gaseous, not rocky, and, therefore, such a collision may not lead to the condensation of a satellite.

Kipping and Teachey noticed unusual anomalies in the transit data of a gas planet, Kepler 1625b, which is several times the size of Jupiter.

The Kepler results were enough for the team to get 40 hours of time with Hubble to intensively study the planet, obtaining data four times more precise than that of Kepler. But everything astronomers know about planets and moons is informed by the makeup of the solar system. There's no analog for such a large moon in our own system. During other orbits, the moon will trail behind its planet, slowing it down and making the transit start later than expected. This particular planet - or exoplanet - is about the same distance from its star as Earth is to the sun.

According to the authors of the study, it's possible that the second dip in light could be caused by another planet orbiting the star, but the Kepler Space Telescope didn't find any evidence of a second planet in the system during its observations of the star. The researchers note that in principle this anomaly could be caused by the gravitational pull of a hypothetical second planet in the system, although Kepler found no evidence for additional planets around the star during its four-year mission.

If indeed a moon, it would be about 2 million miles (3 million kilometers) from its planet and appear twice as big in its sky, as the moon does in ours.

"That's been a key driver for us for a while, just trying to understand the cosmic habitats out there that we might look for, for life", says Kipping.

It's not like the exomoon in "Avatar" or Endor from "Star Wars", Teachey said, "but going forward, I think we're opening doors to finding worlds like that".

Based on the moon's distance from its star, its surface temperature was estimated to be 80C, which is considered just on the upper end of conditions that could support life. They went public with their suspicion after Twitter sleuths pointed out that they had won time on the space telescope. The astronomers are uncertain how this potential moon might have formed, given its size. Other moons, such as Neptune's largest moon Triton, may have been captured from the Kuiper belt.

The capture and impact scenarios are implausible for such a large moon, Kipping said.

"With exomoons we are stretching the limits of our instrument detection thresholds and precision", astronomer Laura Mayorga, who wasn't involved in the new study, said via email. That would confirm that the find is an exomoon.

"If this does pan out and turn into a true discovery, it would be really revolutionary, but I don't think we're quite there yet", says Megan Bedell, an astronomer at the Flatiron Institute in NY.

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